Picture this. While you're picking your groceries, thieves are pickpocketing you. Organized crime is nothing new, but across America these rings are targeting unsuspecting shoppers. Tonight you're going to meet a man who works on the wrong side of the law for the right reasons, to make sure it doesn't happen to you. Here's ABC's Cecilia Vega. Reporter: Shoppers, beware. Inside this San Diego whole foods surveillance video catches a pickpocket in action. Just for a split second the shopper turns away from her cart. And that is all the man in the checkered shirt needs. His hand's covered by a shopping bag, hide what he's about to do. The woman, so distracted by the samples being handed out, has no idea this crook walked away with her wallet and handed it off to a partner. A classic move, says master pickpocket bob Arno. He's got to do it just when she's reaching. That is when she's most vulnerable. Reporter: Over in the produce aisle these thieves play a game of double distraction. One talks to this store employee to get him to turn away. His partner in the row behind him moves in. As the woman in the hat looks away from her cart to pick the perfect apple, he picks up her wallet. She's getting her fruit. He's getting her purse. He's got it. Reporter: Police released these surveillance videos to San Diego affiliate KGTV hoping they'd lead to an arrest. All around the country theft rings run by sticky-fingered pickpockets are making a killing targeting unsuspecting people. The thieves analyze you very well. They are like a school of fish swimming. And then suddenly watching for the weak nest victim. The one who is not paying attention. So those are yours? Reporter: Arno knows the game. He is, after all, a professional. Thank you. Reporter: But not in the illegal thief, steal your stuff and never see it again way. Bob gives expert advice to law enforcement on how to catch crooks red handed. He took me along to show how to avoid making a pickpocket's job to easy. Here's how it works. As bob and his wife sandy casually distract this group. Watch the woman's purse hanging on a chair. She's so busy talking she has no idea what's going on behind her. Did you take my -- Yeah. We're doing a story on when people are distracted, how easy it can be for someone to reach in your purse like he just did. Did you have any idea what he was doing right behind you? No. Reporter: Now that everyone is on guard, you'd think it wouldn't happen again. But just as bob explains how he got away with it the first time, it happens fast. Watch bob's hand again. It looks like he's leaning on her chair. But her purse is going, going, gone. There are ways to avoid becoming a victim. A tip from this expert pickpocket. Don't be distracted just because someone appears trustworthy. I just assume the best in people. I don't think people are out to get me or out to steal from me. So yeah, it's very surprising and shocking. Reporter: Another warning from bob. If it's easy for you to get to, it's easy for the crooks too. Keep your valuables in the bottom of your bag, not the top. How do you not become a victim? Show me your purse. It's high up under the armpit. Most of mine are even higher, more like this. But this one is fairly safe. It's always hair. It's never behind me like this. Never. And if I'm feeling at all threatened, it will be moved to the front. Reporter: This Bonnie and Clyde on the right side of the law works in a pair, like many pickpockets in it for the wrong reasons. Those thieves in San Diego part of a team. One does the stealing. The others act as a decoy or lookout. I love this scene here because it is teamwork of three and each one in this team has a very precise duty, an exact job. Reporter: And something else. They have props. Whether it's a shopping bag deftly placed over a hand or bob's tool of choice, a coat draped over a shoulder, blocking what's really happening with those fast fingers. What's going on back here? So this man is going to move out here. Now, why? Because now everyone around who sits there will watch it, cannot see what's going on, including the victim. So if I have this like this, we call it a toreador position. Classic. Reporter: Keep an eye on the cell phone on the table. Now you see it. Now you don't. Do you notice anything missing? Food. Do you want to call me and talk about it? You want to talk to me about it? Your phone. Oh, my phone. You didn't even realize while he was talking to you that he got your phone. That's a little nerve-wracking. If you're in a crowded area, in a coffee shop with a lot of foot traffic in a major city, doing that and then stepping up anywhere, it's definitely a no-no. Reporter: And that is bob's most important lesson. Keep everything in your line of sight where you can see it. This woman left her purse all the way on the other side of the store and walked away to make a transaction. Making her a prime target. Did you put that money in your wallet? I put that money in my -- that's my stuff. Guess who looks for you. The professional guys who like that. Next time you go shopping, keep your purse on you, I guess, right? Right. Reporter: Think men's wallets are harder to swipe? Think again. While I talked to this man, bob slides his wallet right out of his front pocket and hands it over. Did you feel it? Did you feel anything? I didn't actually feel it because of all the stuff going on. All the commotion? Yeah. We kind of got you. You see this here? The different angles. That's what the thief is going to look for. The angles of it. The thieves call it the crown of the money. The four corners of your phone or the four corners of your wallet. And I like to do it when you lean. Just stretch for the card. That's what you're paying attention to. The way you carry your wallet? I'll carry it in my shoe next time. Reporter: Well, maybe you don't have to go that far. Just do one thing, bob says. Pay attention. So how much of this is about your quick fingers, and how much of this is about them not paying attention? I think it's more about them not paying attention. Victims make it easy for the thieves. Crime of opportunity. Absolutely. Reporter: For "Nightline" I'm Cecilia Vega in Phoenix.

This transcript has been automatically generated and may not be 100% accurate.

Now Playing: Stripping to Pay For College

Now Playing: How Michael Jackson's Billboard Performance Was Pulled Off

Now Playing: Is a Gluten-Free Diet Really Helpful?

Now Playing: Shelly Sterling: Donald Sterling Has 'Onset of Dementia'

Now Playing: Hidden Cameras Reveal How Pickpockets Snag Valuables

Now Playing: Friends, families mourn Florida high school shooting victims

Now Playing: Drake claims to give away almost $1 million in new music video

Now Playing: A rare, inside look at the personal life of Gloria Allred

Now Playing: {{itm.title}}

{"id":23690860,"title":"Hidden Cameras Reveal How Pickpockets Snag Valuables","duration":"7:00","description":"Shoppers may want to think twice before turning their backs on their purses in shopping carts.","url":"/Nightline/video/hidden-cameras-reveal-pickpockets-snag-valuables-23690860","section":"Nightline","mediaType":"default"}